Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/30/21

Area Forecast Discussion...Updated

National Weather Service Phoenix AZ

 445PM MST Fri Jan 29 2021

.UPDATE...Updated aviation discussion.

&&

.SYNOPSIS...
A fast moving storm system is currently moving through the region.
Isolated morning showers across southeast California are winding
down but scattered showers and an isolated thunderstorm will
continue across southern Arizona through early evening. Cooler
temperatures are settling into the region with highs mostly topping
out in the lower 60s across the lower deserts through Saturday. High
pressure is then forecast to take over late in the weekend into
early next week allowing for a brief warm up before another storm
system impacts the region during the middle of next week.

&&

.DISCUSSION...
Another storm system is moving through the region today bringing
showers, breezy conditions, some high elevation snow, and a few
thunderstorms. The majority of the precipitation will develop this
afternoon over south-central Arizona. Dry conditions were noted this
morning over Phoenix via ACARS soundings, with PWAT values of near
0.4". This afternoon, PWAT will briefly increase to near 0.8" just
ahead of the cold frontal boundary, which has a modest subtropical
moisture tap. As moisture and surface temperatures increase,
instability will also go up, with MUCAPE of 100-200 J likely
developing over the next few hours. HREF guidance suggests that
western Maricopa County and areas south of Phoenix will see the
highest instability values. With that said, showers are already
beginning to consolidate over southwest Arizona, and will continue
to do so as the line of showers moves eastward.

Current timing has slowed somewhat, with showers likely to begin in
the western portions of the Phoenix metro between 2-3 pm, and 3-4 pm
for the rest of the metro area. There will be a window of about 3-5
hours after this when most if not all precipitation will occur.
Winds are expected to be breezy, especially near any showers, but
most locations will see peak gusts below 30 mph. As the showers
move to the east of Phoenix they will result in some locally
heavier rainfall. HREF probabilities show storm totals of
0.50-1.00" over the high terrain, with a 10% probability of
exceeding 1" in 3 hours. This suggests that most likely this will
be a beneficial rain, but isolated impacts (especially over burn
scars) cannot be ruled out. In Phoenix, total precipitation of 0.10"
to about 0.30" can be anticipated for most areas. As for snow,
1-3" will be possible above about 4500 feet, leading to relatively
minimal impacts.

By late in the evening into the overnight hours, the upper level
trough will be quickly exiting into New Mexico allowing for drier
westerly flow aloft to spread across Arizona. Some lingering
cloudiness is likely across eastern Arizona tonight, but much of the
lower deserts should clear out after midnight. The clearing skies,
diminishing winds, and residual boundary layer moisture may create a
fog set-up Saturday morning across Pinal County and maybe into the
outlying Phoenix metro. Have maintained a mention of patchy fog from
central Pinal County northwestward through Buckeye for now.
Overnight lows tonight are likely to dip well into the 40s with many
places likely dipping into the 35-40 degree range.

The rest of the weekend will see improving conditions with mostly
sunny skies, but chilly temperatures on Saturday. A decent warm up
is expected on Sunday with an upper level ridge moving through the
region, as highs are forecast to get close to 70 degrees again.
Later Sunday into Monday, a deepening trough off the Northwest U.S.
coast will turn our flow out of the southwest, pulling up a decent
stream of upper level moisture into our region. Clouds will be
increasing on Sunday with Monday likely being fairly overcast.
Despite fairly cloudy skies on Monday, high temperatures are likely
to top out at or just above 70 degrees as warm southerly flow
continues. Similar conditions are likely for Tuesday, but breezy
conditions are likely to begin as the upper trough to our northwest
approaches the region. WPC cluster analysis reveals that many of the
ensemble members are clustering by their parent model, meaning the
majority of GFS ensemble members are distinct from the ECMWF
ensemble members, and both are distinct from the Canadian ensemble
members. The Canadian ensembles are wanting to partially cut off the
trough, resulting in a wet but warmer and slower solution. The GFS
ensemble members are less amplified, meaning a cool but mostly dry
outcome. The ECMWF ensemble members are more amplified, resulting in
a cool and wet outcome. There is no preferred solution at this time,
but a period of below normal temperatures does seem likely.

&&

.AVIATION...Updated at 2345Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Moderately strong cold front continued to push east and through the
greater Phoenix area late this afternoon; expect to see widespread
showers, some moderate in intensity, through about 02z with CIGS
locally down to around 2k feet. More widespread CIGs in the 4-7k
range. Visibility may drop to 2-4SM at times in moderate showers. As
the front moves off to the east, low cloud decks to scatter out but
there will be lingering SCT-BKN decks in the 4-6k foot range with
isolated lingering instability showers (VCSH). Expect mostly FEW
decks after 06z but down into the 3-5k foot range. With skies
clearing and winds becoming light there may be patchy fog developing
during the morning but confidence is not overly high so will leave
this out of the TAFs for now.

Gusty west wind to around 25kt will taper off after 02z to generally
less than 12kt with winds becoming light/variable or light east
after 06z. Although winds should tend to shift back towards the west
Saturday afternoon speeds should be light and mostly 6kt or less.

As the band of showers moves across the greater Phoenix area through
around 01z, there is potential for some intensification of some of
the cells with lightning/weak storms possible. Should a storm
actually approach one of the terminals it could lead to briefly
strong/gusty and somewhat variable winds but still tending to favor
a westerly component. At TAF issuance time there were no storms
detected within the showers to our west but lighting was detected
further north/northwest into Mohave County. Some hi-res guidance
suggests that isolated weak storms with lightning may develop
withing the band as it moves through; due to low confidence it is
not currently mentioned explicitly in the TAFs but amendments will
be issued should convection intensify and storms threaten the
terminals. Threat should pretty much be over by 02z this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: As
the cold front moves well to the east of the western deserts, only
expect some lingering low/mid cloud into mid evening with FEW-SCT
decks in the 6-10k foot range. Skies should become generally clear
by midnight. Gusty southwest to wind to taper off to mainly below
12kt by 03z. Winds should be on the light side Saturday and there
will be no aviation concerns going forward.

&&

.FIRE WEATHER...
Sunday through Thursday:
Weak high pressure will persist across the region into early next
week with temperatures warming to slightly above normal under
increasing high cloudiness. A potential weather system during the
middle of next week will bring back precip potential, likely
favoring high elevation areas. Winds will be light through Monday,
but breezy to locally windy conditions become possible at times
Tuesday through Thursday. Moisture levels through the period will
remain somewhat elevated with minimum RHs of 25-30% for Sunday and
Monday before rising slightly on Tuesday and possibly Wednesday.
Drier conditions and lower RHs are likely to settle into the
region late next week.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch from 5 PM MST this afternoon through Saturday
     afternoon for AZZ556.

CA...None.
&&

$$

DISCUSSION...Hodges/Kuhlman
AVIATION...CB
FIRE WEATHER...Kuhlman